The overall objective of the proposed research is to develop and use physical methods of membrane biochemistry, together with established immunological procedures, to elucidate immunological phenomena which are controlled by the structure and composition of cell membranes; it is anticipated that this objective will be accomplished through substitution of cells which elicit immune responses by well-defined model membranes and by similar preparations obtained by fractionating and modifying cell membranes. Of particular interest is the development of new biochemical methods for investigating the molecular basis of T cell help and the nature of the T cell antigen receptor.